These mic mixers from the 1960s are slept on (these were purported to be used to mix the mics for the Woodstock '69 festival!)

Today, they can often be found for super cheap or free, and they have pretty great transformers in them for each channel.

I modded this one to have concentric pots on each channel, in/out switches, and separate outs on each channel in addition to mixing to the main output in the stock setup. The outer pot handles the input gain into the transformer, and the inner pot handles the output gain. Works similarly to a trim/gain setup found in higher-end mic preamps.

Essentially, this lets you add transformer iron warmth to synths, groove boxes, or anything else looking for some additional grit.

Super fun box, instant mojo if you're lacking some in your setup.